Effects of instructional constraints on human fixed-interval performance.

Several groups of human subjects were exposed to a variety of experimental conditions involving a fixed-interval 27-second schedule of reinforcement in compound with instructions to constrain in the number of responses within the interreinforcement interval and/or the duration of the experimental session. One group was further exposed to a contingency involving the placement of responses within the IRI. A diversity of patterns of performance was observed, including those typically associated with animal subjects exposed to FI schedules. Generally, the imposition of instructions to minimize session duration reduced post-reinforcement pausing and increased overall reinforcement density from those levels obtained with only instructions to expend a given number of responses per reinforcer. The results are seen to underscore the sensitivity of human fixed-interval performance and the contribution of extra-experimental contingencies.